Expanding bit screw driver



Nov. 3, 1953 E. H. SHAFF EXPANDING BIT SCREW DRIVER Filed Feb. 10

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Patented Nov. 3, 1953 EXPANDING BIT SCREW DRIVER Ernest H. Shafl, Hamilton, Ind.,' assignor to Keller Tool Company, Grand Haven, Mich., a

corporation of Michigan Application February 10, 1951, Serial ism-210,411

The present 1 invention relates generally to screwdrivers and more particularly to screwdrivers'of the type adapted to pick up and retain screwslfor application to the work. l I v It is a general object of theinvention'to provide a screwdriver of the foregoing character which may be easily manipulated, is of simple and rugged construction and which permits of economical manufacture.

The object of the invention thus generally set forth together with other objects and ancillary advantages is attained by the construction and arrangement shown by way of illustration in the accompanying drawing, in which:

Figure l is a fragmentary perspective view of a screwdriver embodying the features of the present invention.

Fig. 2 is a central longitudinal section through the screwdriver illustrated in Fig. 1 and showing the normal relationship of its parts.

Fig. 3 is a sectional view similar to Fig. 2 but showing the relationship of the parts of the screwdriver upon driving a screw.

Fig. 4 is a fragmentary exploded perspective view of the screwdriver bit shown in the preceding figures.

As illustrated in the drawings, the exemplary screwdriver embodying the present invention in cludes a supporting member or shank It on which is slidably mounted a bit I2. The latter is of generally tapered form and is composed of a pair of blades I6 and I8. The outer ends of these blades form kerf engaging faces. Provision is made whereby such faces can be adjustably spaced so as to enable the bit to be snugly received in screw kerfs of various widths.

Preferably the bit blades I6 and I8 are formed of flat spring steel and are shaped to converge toward the axis of the screwdriver, abutting each other at their outer ends. The inner ends of the blades are held in spaced relation by means of a block 20. The blades are fixed to opposite sides of the block 20 and the block serves to support them on the shank I0.

Adjustable spacing of the outer faces of the tip of the bit I2 is afforded through the provision of means to spread the blades I6 and I8 apart. To this end a wedge 24 having a taper substantially corresponding to that of the blades is interposed between them, and the bit I2 is made movable relative thereto so that the wedge tip can be inserted or withdrawn as desired to vary the spacing of the outer ends of the blades. Preferably, the wedge 24 is formed integral with the shank I and the bit I2 is made movable 1 Claim. (Cl. 14550) 2 longitudinally thereof. For this purpose, the block' 20 to which the inner ends of the blades I6 and I8 are fixed is received in an elongated slot 26 formed longitudinally in the shank I0. Thus the block 20 serves as a carrier for the blades I6 and I8 and engagement thereof with the side walls of the slot 26 serves to guide bit movement with respect to the shank III.

Preferably, the tip of the bit 12 is formed to provide substantially parallel kerf engaging faces so that full surface engagement between the bit and the walls of the screw kerf obtains. When there is such engagement, danger of camming the bit from the screw kerf is minimized. For this purpose the outer ends of the blades I6 and I8 are bent laterally outward as at 21 to extend parallel to the bit axis. The inner surfaces of the blade tips lie fiat against each other.

Interp'osed between the block 20 and the inner end of the slot 26 is a compression type spring 28. The spring normally serves to bias the bit I2 outwardly with respect to the shank I4 into the position shown in Fig. 2.

The present invention is shown incorporated in a screwdriver of the hand-held type. For this purpose it is provided with a suitable handle 30. To attach the handle 30 to the bit, rivets 32 are used, one of which is received in a hole 34 adjacent the inner end of the shank I0 and the otherv may be inserted through the inner end of the slot 26. With such a construction, as is illustrated in the accompanying drawing, the inner end of the biasing spring 28 bears against the latter rivet.

Upon inserting the tip of the bit I2 in the kerf of a screw and exerting a force in a direction axially of the screwdriver, the shank I0 is moved forwardly with respect to the bit. Such movement forces the tip of the wedge 24 between the abutting end portions of the blades I6 and I8 and spreads them apart into full surface engagement with the walls of the screw kerf (Fig. 3)

The greater the force exerted, the larger will be the wedging action. This results in increased frictional engagement between the outer faces of the tips of the blades I6 and I8 and the walls of the screw kerf. Because of the spring nature of the blades Is and I8 themselves, the blade tips are constrained to full surface engagement with the kerf walls. Furthermore, because of the elongated tapered form of the bit I2 and the wedge 24, there is a tendency for the wedge to be frictionally held in such position thereby reducing the axial force required to maintain engagement of the bit with the screw kerf. Upon pulling the bit from the screw kerf the spring 28 is efiective to return the blades l6 and i8 to nor mally extended position with respect to the wedge 24.

Still another advantage flows from this construction. The intimate engagement between the wedge 24 and the blades l6 and I8 provides reinforcement for the blades for snbstantially their entire length. Therefore, danger of damaging the bit [2 upon application oi a severe torsional force is minimized.

A screwdriver constructed in accordance the present invention also permits of use to pick up a screw from a receptacle and hold it in posi? tion for application to the work. 290 do so, a

user merely inserts the tip of the bit 12 in the screw kerf and moves the blade r pyyardly the shank I0 against the action of the spring 28 so that the tips of the blades l6 and I8 arespread apart by the wedge 24. The blade tips are thus spread into ,f ictio al en a emen with the her? walls. permit-tine th screw to be seiz d an held in positio tor in ertion the wo k.

I claim s my i vention ,A screw driv r comprisin i cem ipa en shank having an elon a ed l n tudinal y posed slo t erein, a bit inclu ng a pair at flat elongated resilient blades, and an axially elon-v gated carrier block disposed within and longi- 4 tudinally slidable in said shank slot with its sides slidably engaging the sides of said slot to constrain the same to axial movement with respect to said shank, said blades being fixed adjacent their rear ends to said carrier block on opposite sides of said shank and converging toward each other toward their outer ends, said bit being nor- .m y e trr t y osed w t resn s to Said shank, an elongated wedge rigid with said shank outwardly of said slot and interposed between said blades to spread said blades apart upon outward movement of said shank with respect to said bit, and a spring disposed in said slot inweirdly or said blhck, said spring being comgpon outward axial movement of said shank with respect to said bit for restoring said shank. and :bit is!) their normal relative positions.

ERNEST H. SHAFF.

References Cited in the file of this patent STATES PAI'EN'IS 

